THIS invention relates to a method of operating a multi-station communication network, and to a network employing the method.
International patent application no. WO 96/19887 describes a communication network in which individual stations in the network can send messages to other stations by using intermediate stations to relay the message data in an opportunistic manner.
In order to be in a position to send a new message out into the network via a selected one of several possible intermediate stations, or to relay a message onward in the same manner, each station must at any time normally be in contact with several other stations.
To optimise the operation of a network of this kind, the interaction of the individual stations must be regulated according to predetermined criteria, in order to minimise contention or interference between stations while at the same time maximising data throughput at minimum transmission power.
It is an object of the invention to provide a method of operating a multi-station communication network which regulates the connectivity between stations in order to optimise the operation of the network.
According to the invention there is provided a method of operating a communication network comprising a plurality of stations each able to transmit and receive data so that the network can transmit data from an originating station to a destination station via at least one intermediate station, the method comprising:
a) defining at least one calling channel;
b) selecting, at each station and according to first predetermined criteria, a calling channel for the transmission of probe signals to other stations;
c) transmitting probe signals from each station on the selected calling channel, other stations which receive the probe signals from a given station responding directly or indirectly to thereby indicate to the given station their availability as destination or intermediate stations; and
d) evaluating, at the given station, the direct or indirect responses of other stations to said probe signals according to second predetermined criteria, in order to identify other stations with which the given station can communicate optimally.
The other stations receiving the probe signals from the given station may each modify their own probe signals to include data indicating the quality of the communication between the given station and themselves, the given station being responsive to said data to vary at least one parameter of its transmissions so that it can communicate optimally with a desired number of other stations in the network without causing undue contention or interference between stations.
The probe signals from the given station may include data identifying other stations which said given station has detected as being available as destination or intermediate stations..
The probe signals may further include data indicating the quality of the communication between the given station and each other identified station.
The probe signals may be broadcast probe signals addressed to all or a plurality of the other stations.
The probe signals may additionally include addressed probe signals, addressed to at least one other station with which the station transmitting the addressed probe signals wishes to communicate.
The addressed probe signals are preferably transmitted more frequently than the broadcast probe signals.
Typically, the addressed probe signals include age information corresponding to the age of the data indicating the quality of the communication between the given station and each other identified station, for use by the station receiving the addressed probe signals in selecting other stations with which to communicate.
The probe signals may include power gradient information corresponding to the cumulative transmission power required for each identified station to reach those other identified stations with which said each identified station can communicate, for use by the station receiving the probe signals in selecting other stations with which to communicate.
The method may include transmitting chaser signals from an originating to a destination station, the chaser signals following multiple paths to the destination, thereby generating power gradient information usable by stations of the network in selecting a route for the transmission of data from the originating station to the destination station.
A gradient message may be transmitted from the destination station to the originating station, the gradient message including data corresponding to the cumulative power required to transmit a data message from the originating station to the destination station via an optimum route.
Preferably, all messages routed through the network include power gradient information corresponding to the cumulative transmission power required for the message to reach respective stations on its route through the network, thereby to permit optimised routing of messages through the network.
Stations receiving probe signals from the given station may respond by transmitting reply signals to the given station, the given station comparing the number of reply signals received from different stations with a predetermined value, and varying at least one parameter of its transmission if the number of reply signals does not correspond to the second value until the number of reply signals received by the given station corresponds to the predetermined value.
The method may include defining a plurality of calling channels, each calling channel except the first having a higher data rate than a previous calling channel and selecting a different calling channel having a different data rate from the previous calling channel according to the second predetermined criteria if the number of reply signals does not correspond to the predetermined value.
The first predetermined criteria may include the calling channel data rate and/or the calling channel transmission power, the calling channel being selected according to the highest available channel data rate and/or the lowest available channel transmission power.
The second predetermined criteria may include the calling channel data rate and/or the calling channel transmission power, the different calling channel being selected to have an incrementally lower channel data rate and/or an incrementally higher channel transmission power.
The predetermined value, which is compared with the number of reply signals, is preferably calculated to correspond to a desired number of neighbour stations available to a given station as intermediate or destination stations, to permit the given station to communicate optimally with a desired number of other stations in the network without causing undue contention or interference between stations.
The method may include defining a plurality of data channels, each data channel except the first having a higher data capacity than a previous data channel, each station transmitting data to neighbour stations on selected data channels after determining the availability of said neighbour stations.
The data channels may correspond to respective calling channels, a data channel being selected for transmission of data which corresponds to the selected calling channel.
In one version of the method, a plurality of data channels correspond to a single calling channel, the data channels being monitored for activity by the stations and a station wishing to transmit data selecting a data channel which has been detected as free of activity, thereby to optimise data channel usage between stations.
The probe signals transmitted by each station on the calling channels preferably include information indicative of the intention of a given station transmitting said probe signals to move to a selected data channel which is then flagged as being active, to permit other stations to communicate successfully with the given station on the selected data channel.
The probe signals may be transmitted regularly by stations attempting to establish contact with other stations, other stations receiving the probe signals responding to a random number of the probe signals, said random number being equal to or less than the number of probe signals transmitted.
The method preferably includes controlling, at each station, the interval between the transmission of probe signals by a probe timer, the probe timer defining an interval between successive probe signals which is longer than the duration of a probe signal, and transmitting response signals during periods between the successive probe signals.
The interval between the transmission of successive probe signals at each station may be varied according to whether or not the station has data to transmit, the probe timer defining a first, relatively short interval between successive probe signals when the station has data to send, and a second, relatively long interval between successive probe signals when the station has no data to send.
Designated important stations may transmit probe signals including data identifying them, other stations receiving these probe signals in turn modifying their own probe signals to include the data identifying the important stations, so that even stations remote from the important stations obtain said data.
The designated important stations may include, for example, gateway stations, certification authority stations and, from time to time, originating or destination stations.
The method may include distributing updated software for the operation of the stations by uploading the updated software to a selected station, and distributing portions of the updated software to other stations until each other station has the complete updated software.
The updated software is preferably distributed in update blocks including version data and block number data to permit stations to assemble the update software from a plurality of received update blocks.
Preferably, at least one of the update blocks includes timing data indicating a date and time at which the updated software must be used.
The invention extends to communication network comprising a plurality of stations each able to transmit and receive data so that the network can transmit data from an originating station to a destination station via at least one intermediate station, each of the stations operating in use to:
a) define at least one calling channel;
b) select, according to first predetermined criteria, a calling channel for the transmission of probe signals to other stations;
c) transmit probe signals to other stations on the selected calling channel, other stations which receive the probe signals from a given station responding directly or indirectly to thereby indicate to the given station their availability as destination or intermediate stations; and
d) evaluate the direct or indirect responses of other stations to said probe signals according to second predetermined criteria, in order to identify other stations with which the given station can communicate optimally.